A typical loudspeaker is difficult to mount within a ceiling structure. Special ceiling loudspeakers exist which include some sort of mounting device that allows them to be affixed to a ceiling. An example of such a loudspeaker system is disclosed in U.S. Pat. No. 5,088,574, entitled CEILING SPEAKER SYSTEM, issued on Feb. 18, 1992 to Kertesz. Flush mountable ceiling speakers are loudspeakers that are mounted within a hole in a ceiling such that the front of the speaker is substantially coplanar with the surface of the ceiling. An example of such a loudspeaker is disclosed in U.S. Pat. No. 4,123,621, entitled ACOUSTICAL SPEAKER DEVICE, issued to Walker on Oct. 31, 1978.
A typical ceiling loudspeaker is a two-way system having a lower-frequency transducer that reproduces the lower frequencies and a high-frequency transducer that reproduces the higher frequencies.
One method to increase the lower-frequency output of the lower-frequency transducer is by the addition of a port to the enclosure of the lower-frequency transducer. Low frequencies are then produced not only by the movement of the lower-frequency transducer but also by the movement of air through the port. In a flush mounted ceiling speaker, the port must be on the front of the speaker in order to project the lower-frequency energy in a downward direction toward the audience rather than into the airspace above the ceiling where it will not be heard.
Another feature often incorporated into a ceiling speaker is a line transformer, which allows many speakers in a room to be powered by one amplifier. Such a loudspeaker system often includes an adjustable switch that must be accessible in order to permit the user to change the setting of the line transformer. This adjustable switch should be easily accessible at the point of speaker installation. In the case of a flush mounted ceiling speaker, the most convenient place to access this switch once the speaker is installed is on the front of the speaker.
In some loudspeaker systems the lower-frequency transducer and high-frequency transducer are mounted in a spaced apart relationship in which their various axes and planes are neither coaxial nor coplanar. An example of such a loudspeaker system is disclosed in U.S. Pat. No. 6,411,718, entitled SOUND REPRODUCTION EMPLOYING UNITY SUMMATION APERTURE LOUDSPEAKERS, issued on Jun. 25, 2002 to Danley et al. In other types of loudspeaker systems the high-frequency transducer is mounted coaxially with the lower-frequency transducer. This coaxial mounting method saves space and often provides a relatively smoother transition between lower frequencies and high frequencies when the listener is positioned off axis from the loudspeaker. In some instances the high-frequency transducer will include a horn, also known as a waveguide, in order to control the dispersion pattern of sound emanating from the loudspeaker system. An example of a coaxial speaker system including a waveguide is disclosed in U.S. Pat. No. 6,431,309, entitled LOUDSPEAKER SYSTEM, issued on Aug. 13, 2002 to Coffin.
The higher frequencies at which high-frequency transducer waveguides are effective contain only a portion of the frequencies where intelligible speech is typically present. The human voice produces sounds that appear in the frequency spectrum from between around 100 Hz to 10,000 Hz, with the majority of the vocal intelligibility residing between 500 Hz and 8000 Hz. The typical ceiling speaker includes a lower-frequency transducer that will reproduce a range of frequencies from below 100 Hz up to between 2000 and 4000 Hz (the lower and medium frequencies). The high-frequency transducer in such a speaker will typically reproduce the frequencies from between around 2000 and 4000 Hz up to 20,000 Hz (the high frequencies). The high-frequency transducer often does not produce high levels of sound in the frequency band below 2000 Hz. The high-frequency waveguide that controls the high-frequency transducer dispersion pattern is only effective over the frequency range of the high-frequency transducer to which it is coupled. Such an arrangement leaves the low and medium frequencies produced by the lower-frequency transducer, including those encompassing a significant portion of the human vocal spectrum, with an uncontrolled dispersion pattern.
The resultant −6 decibel beamwidth as a function of frequency for a typical prior art loudspeaker is depicted in FIG. 1. The main area of interest is from about 800 Hz to approximately 2.5 KHz, above which the high-frequency transducer's waveguide begins to control its dispersion pattern. As seen in FIG. 1, the beamwidth between point 1 (800 Hz) and point 2 (2.5 KHz) remains at a value of approximately 200 degrees, which is undesirably large compared to a beamwidth between 50 and 100 degrees for the frequency band above 4000 Hz. When the listener is located beyond some relatively minimal distance from the loudspeaker, the high frequencies occupying the spectrum at 3000 Hz and above will be focused on the listener to a greater degree than the band of frequencies below 3000 Hz, resulting in a large portion of the vocal intelligibility and musical detail being lost.
The directivity index (DI) and directivity factor (Q) for a typical prior art loudspeaker is depicted in FIG. 3. The directivity factor expresses the gain in the peak on axis direction with reference to a theoretical omnidirectional source having the same radiated power, while the directivity index is ten times the logarithm of the directivity factor, in decibels. As seen in FIG. 3, the DI and corresponding Q between point 3 (800 Hz) and point 4 (2.5 KHz) is relatively low compared to the higher frequencies, indicating relatively poor directional focus at these frequencies.
Ideally, a flush mounted coaxial ceiling speaker should utilize a waveguide optimized for the medium and lower frequencies produced by the lower-frequency transducer in addition to a waveguide designed for the higher frequencies produced by the high-frequency transducer, thereby increasing vocal intelligibility and the accuracy of musical reproduction when utilized in a high ceiling application. The ideal speaker system should also include a port to increase the lower-frequency output of the speaker, and include a line transformer switch accessible from the front of the speaker.